As an aside, it might be worth investigating if the touch sensor or the entire display module can be powered off instead of just disabling the backlight, as it might save a touch on power.
I'm not entirely sure if this is fixed now, I'd suppose so since the display is off, we'll have to test to be sure.
This is confirmed not fixed as of 2021-03-16 in 1.3.0. Two-finger tap and scroll work when the screen is locked with display on or off.